Response optimization of a three-axis sensitive SERF magnetometer for closed-loop operation

Most triaxial-vectorial magnetic field measurements with spin-exchange relaxation free(SERF)atomic magnetometer(AM)are based on the quasi-steady-state solution of the Bloch equation.However,the responding speed of these methods is greatly limited because the frequency of the modulation signal should be slow enough to ensure the validity of the quasi-steady-state solution.In this work,a new model to describe the response of the three-axis sensitive SERF AM with high modulation frequency is presented and verified.The response of alkali-atomic spin to high-frequency modulation field is further investigated by solving the Bloch equation in a modulation-frequency-dependence manner.This solution is well verified by our experiments and can offer a reference for selection of modulation frequencies.The result shows a potential to achieve a SERF AM operating in a geomagnetic field without heavy aluminum shielding when the modulation frequencies are selected properly.

Simulation of second-order RC equivalent circuit model of lithium battery based on variable resistance and capacitance

With the rise of the electric vehicle industry,as the power source of electric vehicles,lithium battery has become a research hotspot.The state of charge(SOC)estimation and modelling of lithium battery are studied in this paper.The ampere-hour(Ah)integration method based on external characteristics is analyzed,and the open-circuit voltage(OCV)method is studied.The two methods are combined to estimate SOC.Considering the accuracy and complexity of the model,the second-order RC equivalent circuit model of lithium battery is selected.Pulse discharge and exponential fitting of lithium battery are used to obtain corresponding parameters.The simulation is carried out by using fixed resistance capacitance and variable resistance capacitor respectively.The accuracy of variable resistance and capacitance model is 2.9%,which verifies the validity of the proposed model.

Calculation and application of full-wave airborne transient electromagnetic data in electromagnetic detection

Airborne electromagnetic transient method enjoys the advantages of high-efficiency and the high resolution of electromagnetic anomalies,especially suitable for mining detection around goaf areas and deep exploration of minerals.In this paper,we calculated the full-wave airborne transient electromagnetic data,according to the result of numerical research,the advantage of switch-off time response in electromagnetic detection was proofed via experiments.Firstly,based on the full-wave airborne transient electromagnetic system developed by Jilin University(JLU-ATEMI),we proposed a method to compute the full-waveform electromagnetic(EM)data of 3D model using the FDTD approach and convolution algorithm,and verify the calculation by the response of homogenous half-space.Then,through comparison of switch-off-time response and off-time response,we studied the effect of ramp time on anomaly detection.Finally,we arranged two experimental electromagnetic detection,the results indicated that the switch-off-time response can reveal the shallow target more effectively,and the full-waveform airborne electromagnetic system is an effective technique for shallow target detection.

Helicity of harmonic generation and attosecond polarization with bichromatic circularly polarized laser fields

We theoretically investigate the high-order harmonic generation(HHG) of helium atom driven by bichromatic counterrotating circularly polarized laser fields. By changing the intensity ratio of the two driving laser fields, the spectral chirality of the HHG can be controlled. As the intensity ratio increases, the spectral chirality will change from positive-to negativevalue around a large intensity ratio of the two driving fields when the total laser intensity keeps unchanged. However, the sign of the spectral chirality can be changed from positive to negative around a small intensity ratio of the two driving fields when the total laser intensity changes. At this time, we can effectively control the helicity of the harmonic spectrum and the polarization of the resulting attosecond pulses by adjusting the intensity ratio of the two driving laser fields. As the intensity ratio and the total intensity of the driving laser fields increase, the relative intensity of either the left-circularly or right-circularly polarized harmonic can be enhanced. The attosecond pulses can evolve from being elliptical to near linear correspondingly.

Transmitting oscillation suppression of low-Tc SQUID TEM system based on RC serial and multi-parallel capacity snubber circuit

A low-temperature superconducting quantum interference device(low-Tc SQUID)can improve the depth of exploration.However,a low-Tc SQUID may lose its lock owing to oscillations in the current or the occurrence of spikes when the transmitter is switched off.If a low-Tc SQUID loses its lock,it becomes impossible for the low-Tc SQUID TEM system to function normally and stably for a long period of time.This hinders the practical use of the system.In field experiments,the transmitting current is accurately measured,the voltage overshoot and current spike data are recorded,and the gradient of the primary magnetic field at the center of the transmitting loop is calculated.After analyzing the results of field experiments,it was found that when the gradient of the primary magnetic field far exceeds the slew rate of a low-Tc SQUID,the low-Tc SQUID loses its lock.Based on the mechanisms of the transmitting oscillation,an RC serial and multi-parallel capacity snubber circuit used to suppress such oscillation is proposed.The results of simulation and field experiments show that,when using a 100 m×100 m transmitting loop,the gradient of the primary magnetic field is suppressed from 101.4 to 2.4 mT/s with a transmitting current of 40 A,and from 29.6 to 1.4 mT/s with a transmitting current of 20 A.Therefore,it can be concluded that the gradient of the primary magnetic field is below the slew rate of a low-Tc SQUID after adopting the proposed RC serial and multi-parallel capacity snubber circuit.In conclusion,the technique proposed in this paper solves the problem of a lost lock of a low-Tc SQUID,ensuring that the low-Tc SQUID TEM system functions stably for a long period of time,and providing technical assurance for ground TEM exploration at an additional depth.

Anomalous behavior and phase transformation of α-GaOOH nanocrystals under static compression

The structural compression mechanism and compressibility of gallium oxyhydroxide, α -GaOOH, are investigated by in situ synchrotron radiation x-ray diffraction at pressures up to 31.0 GPa by using the diamond anvil cell technique. The α -GaOOH sustains its orthorhombic structure when the pressure is lower than 23.8 GPa. The compression is anisotropic under hydrostatic conditions, with the a-axis being most compressible. The compression proceeds mainly by shrinkage of the void channels formed by the coordination GaO3（OH）3 octahedra of the crystal structure. Anomaly is found in the compression behavior to occur at 14.6 GPa, which is concomitant with the equatorial distortion of the GaO3（OH）3 octahedra. A kink occurs at 14.6 GPa in the plot of finite strain f versus normalized stress F, indicating the change in the bulk compression behavior. The fittings of a second order Birch-Murnaghan equation of state to the P-V data in different pressure ranges result in the bulk moduli B0=199（1） GPa for P 〈 14.6 GPa and B0=167（2） GPa for P 〉 14.6 GPa. As the pressure is increased to about 25.8 GPa, a first-order phase transformation takes place, which is evidenced by the abrupt decrease in the unit cell volume and b and c lattice parameters.

Comparison of sample temperature effect on femtosecond and nanosecond laser-induced breakdown spectroscopy

In this paper,we investigated the emission spectra of plasmas produced from femtosecond and nanosecond laser ablations at different target temperatures in air.A brass was selected as ablated target of the experiment.The results indicated that spectral emission intensity and plasma temperature showed similar trend for femtosecond and nanosecond lasers,and the two parameters were improved by increasing the sample temperature in both cases.Moreover,the temperature of nanosecond laser-excited plasma was higher compared with that of femtosecond laser-excited plasma,and the increase of the plasma temperature in the case of nanosecond laser was more evident.In addition,there was a significant difference in electron density between femtosecond and nanosecond laser-induced plasmas.The electron density for femtosecond laser decreased with increasing the target temperature,while for nanosecond laser,the electron density was almost unchanged at different sample temperatures.

Two-phase early prediction method for remaining useful life of lithium-ion batteries based on a neural network and Gaussian process regression

Lithium-ion batteries(LIBs)are widely used in transportation,energy storage,and other fields.The prediction of the remaining useful life(RUL)of lithium batteries not only provides a reference for health management but also serves as a basis for assessing the residual value of the battery.In order to improve the prediction accuracy of the RUL of LIBs,a two-phase RUL early prediction method combining neural network and Gaussian process regression(GPR)is proposed.In the initial phase,the features related to the capacity degradation of LIBs are utilized to train the neural network model,which is used to predict the initial cycle lifetime of 124 LIBs.The Pearson coefficient’s two most significant characteristic factors and the predicted normalized lifetime form a 3D space.The Euclidean distance between the test dataset and each cell in the training dataset and validation dataset is calculated,and the shortest distance is considered to have a similar degradation pattern,which is used to determine the initial Dual Exponential Model(DEM).In the second phase,GPR uses the DEM as the initial parameter to predict each test set’s early RUL(ERUL).By testing four batteries under different working conditions,the RMSE of all capacity estimation is less than 1.2%,and the accuracy percentage(AP)of remaining life prediction is more than 98%.Experiments show that the method does not need human intervention and has high prediction accuracy.

Rock and Soil Classification Using PLS-DA and SVM Combined with a Laser-Induced Breakdown Spectroscopy Library

Laser-induced breakdown spectroscopy （LIBS） has become a powerful technology in geological applications. The correct identification of rocks and soils is critical to many geological projects. In this study, LIBS database software with a user-friendly and intuitive interface is developed based on Windows, consisting of a database module and a sample identification module. The database module includes a basic database containing LIBS persistent lines for elements and a dedicated geological database containing LIBS emission lines for several rock and soil reference standards. The module allows easy use of the data. A sample identification module based on partial least squares discriminant analysis （PLS-DA） or support vector machine （SVM） algorithms enables users to classify groups of unknown spectra. The developed system was used to classify rock and soil data sets in a dedicated database and the results demonstrate that the system is capable of fast and accurate classification of rocks and soils, and is thus useful for the detection of geological materials.

Noise cancellation of a multi-reference full-wave magnetic resonance sounding signal based on a modified sigmoid variable step size least mean square algorithm

Nano-volt magnetic resonance sounding(MRS) signals are sufficiently weak so that during the actual measurement, they are affected by environmental electromagnetic noise, leading to inaccuracy of the extracted characteristic parameters and hindering effective inverse interpretation. Considering the complexity and non-homogeneous spatial distribution of environmental noise and based on the theory of adaptive noise cancellation, a model system for noise cancellation using multi-reference coils was constructed to receive MRS signals. The feasibility of this system with theoretical calculation and experiments was analyzed and a modified sigmoid variable step size least mean square(SVSLMS) algorithm for noise cancellation was presented. The simulation results show that, the multi-reference coil method performs better than the single one on both signal-to-noise ratio(SNR) improvement and signal waveform optimization after filtering, under the condition of different noise correlations in the reference coils and primary detecting coils and different SNRs. In particular, when the noise correlation is poor and the SNR<0, the SNR can be improved by more than 8 dB after filtering with multi-reference coils. And the average fitting errors for initial amplitude and relaxation time are within 5%. Compared with the normalized least mean square(NLMS) algorithm and multichannel Wiener filter and processing field test data, the effectiveness of the proposed method is verified.

Determination of Direction of Arrival of Seismic Wave by a Single Tri-axial Fiber Optic Geophone

A fiber Bragg grating (FBG) geophone and a surface seismic wave-based algorithm for detecting the direction of arrival (DOA) are described. The operational principle of FBG geophone is introduced and illustrated with systematic experimental data, demonstrating an improved FBG geophone with many advantages over the conventional geophones. An innovative, robust, and simple algorithm is developed for obtaining the bearing information on the seismic events, such as people walking, or vehicles moving. Such DOA estimate is based on the interactions and projections of surface-propagating seismic waves generated by the moving personnel or vehicles with a single tri-axial seismic sensor based on FBGs. Of particular interest is the case when the distance between the source of the seismic wave and the detector is less than or comparable to one wavelength (less than 100 m), corresponding to near-field detection, where an effective method of DOA finding lacks.

Crustal structure beneath Liaoning province and the Bohai Sea and its adjacent region in China based on ambient noise tomography

The velocity structure of the crust beneath Liaoning province and the Bohai sea in China was imaged using ambient seismic noise recorded by 73 regional broadband stations. All available three-component time series from the 12-month span between January and December 2013 were cross-correlated to yield empirical Green＇s functions for Rayleigh and Love waves. Phase- velocity dispersion curves for the Rayleigh waves and the Love waves were measured by applying the frequency- time analysis method. Dispersion measurements of the Rayleigh wave and the Love wave were then utilized to construct 2D phase-velocity maps for the Rayleigh wave at 8-35 s periods and the Love wave at 9-32 s periods, respectively. Both Rayleigh and Love phase-velocity maps show significant lateral variations that are correlated well with known geological features and tectonics units in the study region. Next, phase dispersion curves of the Rayleigh wave and the Love wave extracted from each cell of the 2D Rayleigh wave and Love wave phase-velocity maps, respectively, were inverted simultaneously to determine the 3D shear wave velocity structures. The horizontal shear wave velocity images clearly and intuitively exhibit that the earthquake swarms in the Haicheng region and the Tangshan region are mainly clustered in the transition zone between the low- and high-velocity zones in the upper crust, coinciding with fault zones, and their distribution is very closely associated with these faults. The vertical shear wave velocity image reveals that the lower crust downward to the uppermost mantle is featured by distinctly high velocities, with even a high-velocity thinner layer existing at the bottom of the lower crust near Moho in central and northern the Bohai sea along the Tanlu fault, and these phenomena could be caused by the intrusion of mantle material, indicating the Tanlu fault could be just as the uprising channel of deep materials.

Application on drilling parameter monitor in drilling engineering monitoring

The drilling parameter monitor is an important tool in drilling engineering applied to monitoring drilling process,carrying out scientific analysis and decision--making.Based on discussing the present development situation of the domestic and foreign drilling machine parameter monitors,the metering scheme for vehicle--loaded drilling parameter monitor was designed.By using detection system for MSP430 single--chip microcomputer(SCM) in combination with peripheral circuit such as sensors,the drilling--rig control system was obtained to detect,and for every parameter in real--time display in order to keep operating the drilling rig status.The experiment shows that the drilling parameter monitor reaches design requirements and can be applied to drilling engineering monitoring,which has characters such as simple structure,high credibility and low cost.

Review of Fiber-optic Distributed Acoustic Sensing Technology

A distributed optical-fiber acoustic sensor is an acoustic sensor that uses the optical fiber itself as a photosensitive medium,and is based on Rayleigh backscattering in an optical fiber.The sensor is widely used in the safety monitoring of oil and gas pipelines,the classification of weak acoustic signals,defense,seismic prospecting,and other fields.In the field of seismic prospecting,distributed optical-fiber acoustic sensing(DAS)will gradually replace the use of the traditional geophone.The present paper mainly expounds the recent application of DAS,and summarizes recent research achievements of DAS in resource exploration,intrusion monitoring,pattern recognition,and other fields and various DAS system structures.It is found that the high-sensitivity and long-distance sensing capabilities of DAS play a role in the extensive monitoring applications of DAS in engineering.The future application and development of DAS technology are examined,with the hope of promoting the wider application of the DAS technology,which benefits engineering and society.

A review of geoanalytical databases

Geoanalytical data provide fundamental information according to which the Earth's resources can be known and exploited to support human life and development.Large amounts of manpower and material and financial resources have been invested to acquire a wealth of geoanalytical data over the past 40 years.However,these data are usually managed by individual researchers and are preserved in an ad hoc manner without metadata that provide the necessary context for interpretation and data integration requirements.In this scenario,fewer data,except for published data,can be reutilized by geological researchers.Many geoanalytical databases have been constructed to collect existing data and to facilitate their use.These databases are useful tools for preserving,managing,and sharing data for geological research,and provide various data repositories to support geological studies.Since these databases are dispersed and diverse,it is difficult for researchers to make full use of them.This contribution provides an introduction on available geoanalytical databases.The database content can be made accessible to researchers,the ways in which this can be done,and the functionalities that can be used are illustrated in detail.Moreover,constraints that have limited the reutilization of geoanalytical data and creation of more advanced geoanalytical databases are discussed.

Anomalous phase transition of InN nanowires under high pressure

Uniform InN nanowires were studied under pressures up to 35.5 GPa by using in situ synchrotron radiation x-ray diffraction technique at room temperature. An anomalous phase transition behavior has been discovered. Contrary to the results in the literature, which indicated that In N undergoes a fully reversible phase transition from the wurtzite structure to the rocksalt type structure, the In N nanowires in this study unusually showed a partially irreversible phase transition. The released sample contained the metastable rocksalt phase as well as the starting wurtzite one. The experimental findings of this study also reveal the potentiality of high pressure techniques to synthesize In N nanomaterials with the metastable rocksalt type structure, in addition to the generally obtained zincblende type one.

Research on the Motion Track of Ocean Towing System

In this paper, a method for predicting the position of towline is presented. The location of the finite node is determined by installing fixed spaced attitude sensors in towline arrays, then the appropriate objective functions are selected for water depth profile and course profile respectively, and the interpolation fitting method is combined with the determined predicted positions. Through the hydrodynamic analysis of the existing towing cable’s underwater motion, the position of the towing cable under the steady state motion is obtained as the reference basis, and two methods are put forward, which are improved spline interpolation method, polynomial fitting method and multivariate nonlinear regression analysis. In the case of steady state motion, the two methods are compared and compared with the hydrodynamic simulation results. Finally, a more suitable method is selected as the basis of cable location inversion and applied to deep-sea towing operations.

Modeling of contact temperatures and their influence on the tribological performance of PEEK and PTFE in a dual-pin-ondisk tribometer

The direct blending of polyether ether ketone(PEEK)with a solid lubricant such as polytetrafluoroethylene(PTFE)improves its tribological performance,but compromises its outstanding mechanical properties and processability.While these negative effects might be circumvented via the hybrid wear method,the influence of the contact temperature between multiple sliding components acting together is not fully understood.Herein,an analytical temperature model considering the influence of both micro-and macro-thermal behavior is extended to predict the contact temperature of a dual-pin-on-disk hybrid wear system.The interactions between several heat sources are investigated and experimentally verified.The analytical results show that the nominal temperature rise of the shared wear track is determined by the combined effect of the heat generated by both pin components,while the rise in flash temperature at the region in contact with each pin component is dependent upon its individual characteristics and working conditions.Hence,while different temperature peaks can coexist in the shared wear track,the maximum value dominates the performance of the system.For the experimentally investigated PEEK–PTFE–steel hybrid wear system,the formation of tribofilms is blocked,and the hybrid wear system fails,when the peak temperature exceeds the glass transition temperature of both pins due to an increase in applied load.

Velocity calibration for microseismic event location using surface data

Because surface-based monitoring of hydraulic fracturing is not restricted by borehole geometry or the difficulties in maintaining subsurface equipment, it is becoming an increasingly common part of microseismic monitoring. The ability to determine an accurate velocity model for the monitored area directly affects the accuracy of microseismic event locations. However, velocity model calibration for location with surface instruments is difficult for several reasons： well log measurements are often inaccurate or incomplete, yielding intractable models; ori- gin times of perforation shots are not always accurate; and the non-uniqueness of velocity models obtained by inver- sion becomes especially problematic when only perforation shots are used. In this paper, we propose a new approach to overcome these limitations. We establish an initial velocity model from well logging data, and then use the root mean square （RMS） error of double-difference arrival times as a proxy measure for the misfit between the well log velocity model and the true velocity structure of the medium. Double-difference RMS errors are reduced by using a very fast simulated annealing for model perturbance, and a sample set of double-difference RMS errors is then selec- ted to determine an empirical threshold. This threshold value is set near the minimum RMS of the selected samples, and an appropriate number of travel times within the threshold range are chosen. The corresponding velocity models are then used to relocate the perforation-shot. We use the velocity model with the smallest relative location errors as the basis for microseismic location. Numerical analysis with exact input velocity models shows that although large differences exist between the calculated and true velocity models, perforation shots can still be located to their actual positions with the proposed technique; the location inaccuracy of the perforation is 〈2 m. Further tests on field data demonstrate the validity of this technique.

Review:Progress in SQUID⁃Based Geophysical Precision Measurement Technology

Superconducting quantum interference device(SQUID),with the advantages of ultra⁃high sensitivity,low noise,broad frequency bandwidth,and excellent low⁃frequency response,is widely used in several geophysical methods,such as vector magnetic survey,electromagnetic method,gravity and gravity gradient measurement.In this paper,the latest technological progress of SQUID and SQUID⁃based geophysical precision measurement technology are described.In addition,the advantages,characteristics,and existing problems of each measurement technology are analyzed.Combined with the requirements of current geophysical technology,the future application prospect is discussed and development suggestions are given.